Abstract

Question

Is prehospital thrombolysis more effective than in-hospital thrombolysis for decreasing
short-term mortality in patients with acute myocardial infarction (MI)?

Data sources

Studies were identified by searching MEDLINE, EMBASE, and Science Citation Index (1982 to 1999); Dissertation Abstracts (1987 to 1999); and Current Contents (1994 to 1999) with the terms thrombolysis, thrombolysis therapy, prehospital, and
acute myocardial infarction and with the Cochrane search strategy. Bibliographies
of relevant papers were searched, the U.S. National Institutes of Health Web site
was reviewed, and authors and manufacturers of thrombolytic agents were contacted.

Study selection

Randomized controlled trials were selected if they compared prehospital with in-hospital
thrombolysis for patients with MI and assessed all-cause hospital mortality.

Data extraction

Data were extracted on trial quality, patient characteristics, provider and type of
thrombolytic agent, time from symptom onset to thrombolyis, and outcomes.

Main results

6 randomized controlled trials and 3 follow-up studies (6434 patients) met the selection
criteria. Thrombolytic agents used included urokinase (1 study), anistreplase (3 studies),
and recombinant tissue-type plasminogen activator (2 studies). Providers of thrombolytic
agents included paramedics (1 study), general practitioners (1 study), and a mobile
intensive-care unit (4 studies). The type of thrombolytic agent used and the level
of provider training did not affect the outcomes. Prehospital thrombolysis was associated
with a shorter time from symptom onset to treatment (162 vs 104 min, P = 0.007) and a lower risk for all-cause hospital mortality (P = 0.03) than was in-hospital thrombolysis (Table); prehospital and in-hospital
thrombolysis did not differ for rates of 1 or 2-year mortality.

*Abbreviations defined in Glossary; RRR, NNT, and CI calculated from data in article. Duration of follow-up was not
available.

Commentary

Emergent reperfusion by thrombolytic or mechanical treatment has become the standard
of care for patients with MI. Numerous studies have shown the importance of early
treatment. This finding has led to efforts to educate patients about seeking earlier
treatment and to reduce the time spent in triage once patients have arrived at a treatment
facility.

Given that time is an important variable, taking treatment to the patient is 1 possible
strategy for reducing mortality. Studies of prehospital thrombolysis have shown nonstatistically
significant reductions in in-hospital mortality. Morrison and colleagues have done
a careful review and meta-analysis of randomized trials that compare prehospital and
in-hospital thrombolysis. They report a 16% relative risk reduction in hospital mortality
for patients treated with prehospital rather than with in-hospital thrombolytics.
This reduction is similar to that reported between differing thrombolytic regimens
in the Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded
Coronary Arteries (GUSTO) trial (1).

The meta-analysis by Morrison and colleagues suggests that a strategy of prehospital
thrombolysis has merit, but how to apply this information in an era of changing thrombolytic
agents and increasing use of mechanical treatments is a difficult problem. Where transport
times are short, a prehospital electrocardiogram could speed diagnosis. Treatment
could then be delivered quickly at the receiving facility. Where transport times are
longer, such as in rural areas, a prehospital strategy appears to be most useful.
Delivery of treatment in the field would require a coordinated emergency-medical-system
approach with well-trained personnel, good treatment protocols, and careful tracking
of results.